6-inch, 3 calibers long, weight 100 lb, charge 11/2 lb.
8 " " " 250 " 3 "
10 " " " 500 " 51/2 "
12 " " " 850 " 11 "
The chief efficiency of small quantities of high explosives having
reduced itself to the case of armor-piercing projectiles, it next
became evident that there was an entirely new field for high
explosives into which powder had entered but little, and this was the
introduction of huge torpedo shells, which did nor rely for their
efficiency upon the dispersion of the pieces of the shell, but upon
the devastating force of the bursting charge itself upon everything
within the radius of its explosive effect. It is in this field that we
may look for the most remarkable results, and it is here that the
absolute power of the explosive thrown is of the utmost importance,
provided that it can be safely used. Attention was at once turned in
Europe to the manufacture of large projectiles with great capacity for
bursting charges, and it has resulted in the production of a class of
shells 41/2 to 6 calibers long, with walls only 0.4 of an inch thick.
(If they are made thinner, they will swell and jam in the gun when
fired.)
These shells are used in long guns up to 6 and 81/2 inches caliber, and
in mortars up to 11.2 inches. They are made from disks of steel, 3 to
4 feet in diameter and 1 inch thick, and are forced into shape by
hydraulic presses. The base is usually screwed in, but some of the
German shell are made in two halves which screw together. The Italians
were the first in this new field of investigation, but the Germans
soon followed, and after trying various materials were at length
reasonably successful with gun-cotton soaked in paraffin. Their 8.4
inch mortar shells of 5 calibers contain 42 pounds; those of 6
calibers contain 57 pounds; and the 11.2 inch mortar shells of 5
calibers contain 110 pounds.
The projectile velocity used with the mortars is about 800 f.s. The
effect of these shells against ordinary masonry and earth
fortifications is very great. The charge of forty-two pounds has
broken through a masonry vault of three feet four inches thick,
covered with two feet eight inches of cement and with three to five
feet of earth over all. The shell containing fifty-seven pounds, at a
range of two and one-half miles, broke through a similar vault covered
with ten feet of earth; but with seventeen feet of earth the vault
resisted. In 1883, experiments at Kummersdorf showed that a shell
containing the fifty-seven pound charge would excavate in sand a
crater sixteen feet in diameter and eight feet deep, with a capacity
of twenty-two cubic yards. The Italians have had similar experiences;
but it is notable that in both Germany and Italy several guns and
mortars have burst. The velocity in the guns is not believed to exceed
1,200 to 1,300 f.s., and it is not thought that the quantity of
gun-cotton is as great in the gun shells as in the mortars. I have
lately been informed on good authority that the use of gun-cotton
shells has been abandoned in the German navy as too dangerous.
The French, in their investigations in this field, found gun-cotton
too inconvenient, and decided upon melenite. This substance has
probably attracted more attention in the military world than all
others combined, on account of the fabulous qualities that have been
ascribed to it. Its composition was for a long time entirely a secret;
but it is now thought to consist principally of picric acid, which is
formed by the action of nitric acid upon phenol or phenyillic alcohol,
a constituent of coal tar. The actual nature of melenite is not
positively known, as the French government, after buying it from the
inventor, Turpin, are said to have added other articles and improved
it. This is probable, since French experiments in firing against a
partially armored vessel, the Bellequense, developed an enormous
destructive effect, while the English, who afterward bought it,
conducted similar experiments against the Resistance, and obtained no
better results than with powder. The proof that the Bellequense
experiments were deemed of great value by the French lies in the fact
that they immediately laid down a frigate--Dupuy de Lome--in which
four-inch armor is used, not only on the side, but about the gun
stations, to protect the men; this thickness having been found
sufficient to keep out melenite shell. In most armorclads, the armor
is very heavy about the vitals, but the guns are frequently much
exposed.
The best authenticated composition for melenite consists of picric
acid, gun cotton and gum arabic, and lately it is stated that the
French have added cresilite to it. Cresilite is another product of
coal tar. Melenite is normally only three times as strong as
gunpowder; but it is said to owe its destructive qualities in shells
to the powerful character of the exploder which ignites it. It has
been known for some years that all explosives (including gunpowder)
are capable of two orders of explosion according as they are merely
ignited or excited by a weak fuse or as they are powerfully shocked by
a more vigorous excitant. Fulminate of mercury has been found most
serviceable for the latter purpose. With melenite the French have
reproduced all the results that the Germans have effected with
gun-cotton and have found that a shell containing 119 pounds of it
will penetrate nearly ten feet of solid cement, but will not penetrate
armored turrets six to eight inches thick. The French claim that
melenite has an advantage over gun-cotton in not being so dangerous to
handle and being insensible to shock or friction, and they have
obtained a velocity of 1,300 f.s. with the 88 inch mortar and claim to
have obtained 2,000 f.s. in long guns up to 62 inch caliber. However
this may be, they are known to have had severe accidents at the
manufactory at Belfort and at least one 56 inch gun was burst at the
Bellequense experiments in firing a sixty-six pound shell containing
twenty-eight pounds of melenite. The French are said to have large
quantities of melenite shells in store, but they are not issued to
service.
Probably one reason why we have so many conflicting yet positive
accounts of great successes in Europe with torpedo shells is because
each nation wishes its neighbors to think that it is prepared for all
eventualities, and they are obliged to keep on hand large quantities
of some explosive, whether they have confidence in it or not.
Fortunately we are not so situated, but singularly enough what we have
done in the field of high explosive projection has been accomplished
by private enterprise, and we have attacked the problem at exactly the
opposite point from which European nations have undertaken it. While
they have assumed that the powder gun with its powerful and relatively
irregular pressures was a necessity and have endeavored to modify the
explosive to suit it, we have taken the explosive as we have found it,
and have adapted the gun to the explosive. At present the prominent
weapon in this new field is the pneumatic gun, but it is obvious that
steam, carbonic acid gas, ammonia or any other moderate and
regulatable pressure can be used as well as compressed air; it is
merely a question of mechanical convenience.
In throwing small quantities of certain high explosives, powder guns
can be used satisfactorily, but when large quantities are required,
the mechanical system of guns possess numerous advantages. All the
high explosives are subject to premature detonation by shock; each of
them is supposed to have its own peculiar shock to which it is
sensitive; but what this shock may be is at present unknown. We do
know, however, that premature explosions in guns are more liable to
occur when the charge in the shell is large than when it is small.
This is due to the fact that when the gun is fired, the inertia of the
charge in the shell is overcome by a pressure proportional to the mass
and acceleration, which pressure is communicated to the shell charge
by the rear surface of the cavity, and the pressure per unit of mass
will vary inversely as this surface. If, then, the quantity of
explosive in the shell forms a large proportion of the total weight of
the shell, we approach in powder guns a condition of shock to it which
is always dangerous and frequently fatal. The pressure behind the
projectile varies from twelve to fifteen tons per square inch, but it
is liable to rise to seventeen and eighteen tons, and in the present
state of the manufacture of gunpowder we cannot in ordinary guns
regulate it nearer than that. It is not a matter of so much importance
so far as the guns are concerned, when using ordinary projectiles, as
the gun will endure a pressure of from twenty-five to thirty tons per
square inch; but with high explosives in the shell it is a vitally
serious matter. From all I can learn regarding European practice, it
appears that not only are the explosives made sluggish, but the
quantity seldom exceeds thirty per cent. of the weight of the shell,
and the velocities, notwithstanding, are kept very low. In the
pneumatic gun the velocity is low also, but so is the pressure in the
gun. The pressure in the firing reservoir is kept at the relatively
low figure of 1,000 pounds per square inch or less, and the air is
admitted to the chamber of the gun by a balance valve which cuts off
just the quantity of air (within a very few pounds) that is required
to make the shot. The gun is long, and advantage is taken of the
expansion of the air. In no case can the pressure rise in the gun
beyond that in the reservoir.
Up to the present time there have been no accidents in using the most
powerful explosives in their natural state, and in quantities over
fifty per cent. of the weight of the projectile. I have seen
projectiles weighing 950 pounds, and containing 500 pounds of
explosives (300 pounds of the blasting gelatine and 200 pounds of No.
1 dynamite) thrown nearly a mile and exploded after disappearing under
water. According to Gen. Abbot's formula such a projectile would have
sunk any armorclad floating within forty-seven feet of where it
struck. Apparently there is no limit to the percentage of explosive
that can be placed in the shell except the mechanical one of having
the walls thick enough to prevent being crushed by the shock of
discharge. In the large projectiles a transverse diaphragm is
introduced to strengthen the walls and to subdivide the charge.
The development of the pneumatic gun has been attended with some other
important discoveries, which may be of interest. It is well known that
mortar fire is very inaccurate, except at fixed long distances, in
consequence of the high angle, the slowness of flight of the
projectile, the variability of the powder pressure, and the inability
to change the elevation and the charge of powder rapidly. In the
pneumatic gun, the complete control of the pressure remedies the most
important of the mortar's defects and makes the fire accurate from
long ranges down to within a few yards of the gun. It is obvious that
the pressure can be usefully controlled in two ways: (1) by keeping
the elevation of the gun fixed and using a valve that can be set to
cut off any quantity of air, according to the range desired; (2) by
keeping the pressure in the reservoir constant, and using a valve
which will cut off the same quantity of air every time, changing the
elevation of the gun according to the distance. Another important
discovery consists in the application of subcalibered projectiles for
obtaining increased range.
The gun is smooth-bored and a full-sized projectile is a cylinder with
hemispherical ends, to the rear of which is attached a shaft having
metal vanes placed at an angle, which causes the projectile to revolve
round its longer axis during flight. A subcalibered projectile,
however, being of less diameter than the bore of the gun, has the
vanes on its exterior, and is held in the axis of the gun by means of
gas checks which drop off as the projectile leaves the muzzle. The
shock to the explosive is, of course, greater than in the full-sized
projectile, but the increase can be calculated, and so far a dangerous
limit has not been reached. From the fifteen-inch gun with a pressure
of 1,000 pounds per square inch and a velocity of about 800 f.s., a
range of 4,000 yards has been obtained at an elevation of 30° 20, with
a ten-inch subcalibered projectile, about eight calibers long and
weighing 500 pounds. This projectile will contain 220 pounds of
blasting gelatine. With improved full-sized projectiles weighing 1,000
pounds, a range of 2,500 yards will doubtless be obtained.
At elevations below 15° these long projectiles are liable to ricochet,
and what is now wanted is a projectile which will stay under water at
all angles of fall and will run parallel to the surface like a
locomotive torpedo. Such a projectile has yet to be invented; but I
have seen a linked shell, which has been experimented with from a
nine-inch powder gun, that partially meets this condition. It is made
of several sections united by means of rope or electric wire in
lengths of 100 to 150 feet. When fired all sections remain together
for some distance; the rear section then first begins to separate;
then the next, and so on. It is primarily intended to envelop an
enemy's vessel, and to remedy the present uncertainty of elevation in
a gun mounted in a pitching boat; but it is found that when it strikes
the water in its lengthened out condition, it will neither dive nor
ricochet, but will continue for some distance just under the surface
until all momentum is lost, when it will sink. This projectile is at
present crude, and has never been tried loaded, but it will probably
be developed into something useful in time.
I have confined my remarks in the foregoing discussion principally to
such methods of using high explosives in shells as have proved
themselves successful beyond an experimental degree, and practically
they reduce themselves to two, viz., using a sluggish explosive in
small quantities from an ordinary powder gun, and using any explosive
from a pneumatic or other mechanical gun. Naturally, the success of
the latter method will soon induce the manufacture of powders having
an abnormally low maximum pressure. There is undoubtedly a field for
the use of such powders in connection with an air space in the gun to
still further regulate the pressure; but nothing of this sort has yet
been attempted. Many methods of padding the shell have been devised
for reducing the shock in powder guns, but the variability of the
powder pressure is too great to have yet rendered any such method
successful. A method was patented by Gruson in Germany of filling a
shell with the two harmless constituents of an explosive and having
them unite and explode by means of a fulminate fuse on striking an
object. He used for the constituents nitric acid and dinitro-benzine,
and was quite successful; but the system has not met with favor, on
account of the inconvenience. The explosive was about four times as
powerful as gunpowder.
That the advantage of using the most powerful explosives is a real one
can be easily shown. The eight inch pneumatic gun in New York harbor,
with a projectile containing fifty pounds of blasting gelatine and
five pounds of dynamite, easily sunk a schooner at 1,864 yards range
from the torpedo effect of the shell falling alongside it.
This same shell, if filled with gunpowder, would have contained but
twenty-five pounds, and have had but one-ninth the power.
The principal European nations are now building armored turrets sunk
in enormous masses of cement, as a result of their experiences with
gun-cotton and melenite. The fifteen inch pneumatic projectile, which
I described as being capable of sinking an armorclad at forty-seven
feet from where it struck, would have been capable of penetrating
fifty feet of cement had it struck upon a fortification. It was not
only a much larger quantity of high explosive than Europeans have
experimented with, but the explosive itself is probably more than
twice as strong as their gun-cotton and five or six times as strong as
their melenite. In the plans of Gen. Brialmont, one of the most
eminent of European engineers, he allows in his fortifications about
ten feet of cement over casements, magazines, etc. It is evident that
this is insufficient for dynamite shells such as I have described.
At Fort Wagner, a sand work built during our war, Gen. Gillmore
estimated that he threw one pound of metal for every 3.27 pounds of
sand removed. He fired over 122,230 pounds of metal, and one night's
work would have repaired the damage. The new fifteen inch pneumatic
shell will contain 600 pounds of blasting gelatine, and judging from
the German experiments at Kummsdorf, which I have cited, one of these
fifteen inch shells would throw out a prodigious quantity of sand;
either 500 pounds to one of shell, or 2,000 pounds to one of shell,
according as the estimate of Gen. Abbot or of Capt. Zalinski is used.
The former considers that the radius of destructive effect increases
as the square root of the charge; the latter that the area of
destructive effect for this kind of work is directly proportional to
the charge.
The effect of the high explosives upon horizontal armor is very great;
but we have yet to learn how to make it shatter vertical armor. No
fact about high explosives is more curious than this, and there is no
theory to account for it satisfactorily. As previously stated, the
French have found that four inches of vertical armor is ample to keep
out the largest melenite shells, and experiments at Annapolis, in
1884, showed that masses of dynamite No. 1, weighing from seventy-five
to 100 pounds, could be detonated with impunity when hung against a
vertical target composed of a dozen one inch iron plates bolted
together.
In conclusion, I may say that in this country we are prone to think
that the perfection of the methods of throwing high explosives in
shell is vastly in favor of an unprotected nation like ourselves,
because we could easily make it very uncomfortable for any vessels
that might attempt to bombard our sea coast cities.
This is true as far as it goes, but unfortunately the use of high
explosives will not stop there. I lately had explained to me the
details of a system which is certainly not impossible for damaging New
York from the sea by means of dynamite balloons. The inventor simply
proposed to take advantage of the sea breeze which blows toward New
York every summer's afternoon and evening. Without ever coming in
sight of land, he could locate his vessel in such a position that his
balloons would float directly over the city and let fall a ton or two
of dynamite by means of a clock work attachment. The inventor had all
the minor details very plausibly worked out, such as locating by means
of pilot balloons the air currents at the proper height for the large
balloons, automatic arrangements for keeping the balloon at the proper
height after it was let go from the vessel, and so on. His scheme is
nothing but the idea of the drifting or current torpedo, which was so
popular during our war, transferred to the upper air. An automatic
flying machine would be one step farther than this inventor's idea,
and would be an exact parallel in the air to the much dreaded
locomotive water torpedo of to-day. There seems to be no limit to the
possibilities of high explosives when intelligently applied to the
warfare of the future, and the advantage will always be on the side of
the nation that is best prepared to use them.
* * * * *